The disclosure of Japanese Patent Application No. 2000-159226 filed on May 29, 2000, including the specification, drawings, and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to an internal combustion engine having an electromagnetic valve driving mechanism that drives at least one of intake and exhaust valves by means of an electromagnetic force generated by application of a magnetizing current thereto, and to a method of controlling the electromagnetic valve driving mechanism.
2. Description of Related Art
In recent years, in the field of an internal combustion engine installed in an automobile or the like, development of an electromagnetic valve driving mechanism capable of arbitrarily changing timings for opening and closing intake and exhaust valves has been promoted for the purpose of preventing mechanical loss resulting from the driving of the intake and exhaust valves in their opening and closing directions, reducing pumping loss of intake air, improving net thermal efficiency, and so on.
As an example of the electromagnetic driving mechanism, a mechanism having a slider, a closing electromagnet, an opening electromagnet, and an elastic member has been proposed. The slider has a magnetic material and slides in cooperation with intake and exhaust valves. The closing electromagnet generates an electromagnetic force that displaces the slider in its closing direction upon application of a magnetizing current thereto. The opening electromagnet generates an electromagnetic force that displaces the slider in its opening direction upon application of a magnetizing current thereto. The elastic member elastically supports the slider at a neutral position between an opening-side displacement end and a closing-side displacement end.
Because such an electromagnetic valve driving mechanism eliminates the necessity to drive intake and exhaust valves in their opening and closing directions by means of a rotational force of an engine output shaft (crankshaft) as in the case of a conventional valve mechanism, mechanical loss resulting from the driving of the intake and exhaust valves is reduced.
Furthermore, the above-described electromagnetic valve driving mechanism can drive the intake and exhaust valves independently of rotating motions of the engine output shaft, and thus has many advantages including a high degree of freedom in controlling timings for opening and closing the intake and exhaust valves, openings of the intake and exhaust valves, etc.
On the other hand, in an electromagnetic valve driving mechanism as described above, when the slider and the intake and exhaust valves are displaced, friction occurs in sliding portions of the slider and the intake and exhaust valves.
Therefore, the necessity to apply a relatively great amount of magnetizing current to the opening electromagnet and to the closing electromagnet for the purpose of displacing the slider against the friction constitutes a problem.
In order to address such a problem, an electromagnetic valve driving mechanism as disclosed in Japanese Patent Application Laid-Open No. 11-36829 has been proposed. The electromagnetic valve driving mechanism disclosed in this publication has a shaft member for transmitting an electromagnetic force to a valve body, and a bearing portion for slidably holding the shaft member. The electromagnetic driving mechanism has a lubricating oil supplying mechanism that supplies lubricating oil to the bearing portion. Therefore, the occurrence of friction between the shaft member and the bearing portion is suppressed. Thus, precise sliding movements of the shaft member are ensured while reducing an amount of magnetizing current that needs to be applied to the electromagnets.
Lubricating oil supplied to an electromagnetic valve driving mechanism as described above has a feature wherein its viscosity changes depending on a temperature of the lubricating oil. For instance, the viscosity of the lubricating oil increases in proportion to a fall in temperature thereof, whereas the viscosity of the lubricating oil decreases in proportion to a rise in temperature thereof.
Therefore, in an electromagnetic valve driving mechanism as described above, sliding resistance (friction resistance) of a shaft member increases when the lubricating oil is at a low temperature. On the other hand, sliding resistance of the shaft member decreases when the lubricating oil is at a high temperature. As a result, the operation speed of the shaft member changes depending on a temperature of the lubricating oil, and therefore the operation speed of intake and exhaust valves may change depending on a temperature of the lubricating oil.
It is an object of the invention to provide an electromagnetic valve driving mechanism that drives at least one of intake and exhaust valves in opening and closing directions by means of an electromagnetic force while making it possible to reduce changes in opening-and-closing operation speeds of the intake and exhaust valves resulting from a temperature or viscosity of the lubricant that is supplied to a sliding portion of the electromagnetic valve driving mechanism.
An internal combustion engine having an electromagnetic valve driving mechanism according to the invention has a lubricant temperature determining device and a controller that adjusts an amount of magnetizing current supplied to the electromagnetic valve driving mechanism.
The electromagnetic valve driving mechanism drives at least one of the intake and exhaust valves of the internal combustion engine in opening and closing directions by means of an electromagnetic force that is generated upon application of a magnetizing current thereto. The lubricant temperature determining device determines (i.e., it detects or estimates) a temperature of lubricant supplied to a sliding portion of the electromagnetic valve driving mechanism, the intake valve, or the exhaust valve. The controller adjusts an amount of magnetizing current supplied to the electromagnetic valve driving mechanism in accordance with the temperature of the lubricant that has been detected or estimated by the lubricant temperature determining device.
In an internal combustion engine having an electromagnetic valve driving mechanism thus constructed, when an intake valve or an exhaust valve is operated in its opening and closing directions, a lubricant temperature determining device first detects or estimates a temperature of the lubricant. A controller adjusts an amount of magnetizing current to be supplied to the electromagnetic valve driving mechanism in accordance with the temperature of lubricant that has been detected or estimated by the lubricant temperature determining device.
For example, the controller may increase an amount of magnetizing current supplied to the electromagnetic valve driving mechanism in proportion to a decrease in temperature of the lubricant that has been detected or estimated by the lubricant temperature determining device.
In this case, the amount of magnetizing current applied to the electromagnetic valve driving mechanism increases in proportion to a decrease in temperature of the lubricant, i.e., in proportion to an increase in viscosity of the lubricant. On the other hand, the amount of magnetizing current applied to the electromagnetic valve driving mechanism decreases in proportion to an increase in temperature of the lubricant, i.e., in proportion to a decrease in viscosity of the lubricant.
As a result, the electromagnetic valve driving mechanism generates a relatively great electromagnetic force when the lubricant has a high viscosity, and generates a relatively small electromagnetic force when the lubricant has a low viscosity. That is, the intake and exhaust valves are driven with a relatively great electromagnetic force when the lubricant has a high viscosity, and are driven with a relatively small electromagnetic force when the lubricant has a low viscosity.
Thus, the intake and/or exhaust valve is driven with an electromagnetic force which is determined by taking the viscosity of the lubricant into account. Therefore, changes in opening-and-closing operation speeds of the intake and exhaust valves resulting from a temperature or viscosity of the lubricant can be reduced.